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J Med Microbiol 54 (2005), 1117-1125; DOI: 10.1099/jmm.0.46158-0
© 2005 Society for General Microbiology
ISSN 0022-2615

Intrabacterial proton-dependent CagA transport system in Helicobacter pylori

Hong Wu1, Takashi Nakano1, Eriko Daikoku1, Chizuko Morita1, Takehiro Kohno1, Hing H Lian2 and Kouichi Sano1

1Department of Preventive and Social Medicine, Osaka Medical College, 2-7 Daigaku-machi, Takatsuki-shi, Osaka 569-8686, Japan 2Department of Biomedical Science, Faculty of Allied Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abd. Aziz, 50300 Kuala Lumpur, Malaysia

Correspondence Kouichi Sano ksano{at}art.osaka-med.ac.jp

Received 17 May 2005
Accepted 24 August 2005

Helicobacter pylori CagA modifies the signalling of host cells and causes gastric diseases. Although CagA is injected into gastric epithelial cells through the type IV secretion machinery, it remains unclear how CagA is transported towards the machinery in the bacterial cytoplasm. In this study, it was determined that the proton-dependent intracytoplasmic transport system correlates with the priming of CagA secretion from H. pylori. The cytotoxicity of neutral-pH- and acidic-pH-treated H. pylori was examined in the AGS cell line. The amount of phosphorylated CagA in AGS cells incubated with acidic-pH- and neutral-pH-treated H. pylori was determined by enzyme immunoassay and Western blot. The production of CagA and adherence of the treated bacteria were examined by enzyme immunoassay and light microscopy, respectively. To clarify how CagA is transported towards the inner membrane of the treated bacteria, the localization of CagA was analysed by immunoelectron microscopy. The proportion of hummingbird cells in the AGS cell line rapidly increased following the inoculation of acidic-pH-treated H. pylori but increased more slowly with neutral-pH-treated H. pylori, and the phenomenon correlated with the amount of phosphorylated CagA in AGS cells. CagA was densely localized near the inner membrane in the acidic-pH-treated bacterial cytoplasm, but this localization was not observed in the neutral-pH-treated bacterial cytoplasm, suggesting that CagA shifts from the centre to the peripheral portion of the cytoplasm as a result of an extracellular decrease in pH. This phenomenon depended on the presence of UreI, a proton-dependent urea channel, but not on the presence of urea. The pH treatments did not enhance CagA production or the adherence of the bacterium to AGS cells. The authors propose that H. pylori possesses a proton-dependent intracytoplasmic transport system that probably accelerates priming for CagA injection.

Abbreviations: EIA, enzyme immunoassay; PAI, pathogenicity island.






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